Control apparatus and method



Sept. 21, 1937'.

w. M. SCHWEICKART 2,093,649 CONTROL APPARATUS ANDYMETHQD Filed Jan.' 5, 1935 2 Sheets-Sheet 1 8| I f 10 4 V e6 '7 I COLD HOT l nz'rumv 'ro semen 75 15 f 3. 1 65 I I, I8 55.

RETUHN'FROM A RADIATOR" I INVENTO'FI WILLIAM MaSYCH-WEICK-ARJ TORNEYS Patented Sept. 21, 1937 I 2093,6451

CONTROL APPARATUS AND. METHOD William M. Schweickart, Euclid, Ohio, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application January 5, 1935, Serial No. 532

8 Claims. (Cl. 2369) The present invention relates toan improved Another object of the invention is the provimethod and system by which a condition or force sion of a condition or force changing system, in may be maintained more nearly at the desired which a condition or force changing device is value than has been possible by prior systems placed in operation by a first control device reand methods. sponsive to actual values of a first condition or One of the objects of the present invention is force and then maintained in operation by means the provision of a system for controllingthe value of a second control device responsive to changes '01 a conditionor force in which a condition or in another condition or force, or responsive to 10 force changing device is controlled by the cochanges in the effectiveness of the condition or m operative action of two devices, one of which reforce changing device. In the preferred embodisponds to one condition or force and the other ment of the invention, the control of the condiof which responds to changes in another condition or force changing device is returned to the tion or force produced directlyby the'condition first control device after the other condition or UNITED STATES PATENT OFFICE or force changing means or responds to changes force or the effectiveness of the condition or in the effectiveness of the condition or force force changing device has changed in-.one direcchanging means, such changes having no definite tion a predetermined amount. Also, preferably, relation to the actual value of the condition, the arrangement is such that the first control force, or efiectivenesa. I device is incapable of placing the condition or In the particular embodiment of the invention force changing device in operation until the other to be hereinafter described, the condition or'force condition or force, or the effectiveness of the con- 20 changing device takes the form of a temperature dition or force changing device, has changed at changer and particularly a heater, such as a least a predetermined amount in the opposite boller'fired by any suitable means, for instance, direction. the well known electrically operated coal stoker. The system of the present invention has par- 5 The condition to which .one of the control deticular utility in connection with control systems ,vices responds is a temperature condition and including a sensitive single circuit switching may well be the temperature of a space to be mechanism for controlling a relay. Such syscontrolled. The other control device, in the case terns, while extremely sensitive, are often objecof, a heatingsystem, responds to changes in some tionable in that their extreme sensitiveness often condition directly produced by the heater such as results in a rapid energization and deenergiza- 30 changes in heater temperature or pressure, altion ofthe relay, commonly called relay chatthough in the preferred embodiment of the inter. In the present system, the relay is initially vention, this device responds to changes in stack energized by the closure or a, sensitive single cir temperature. Inorder to renderthis second concuit switching mechanism. The relay isthen trol device responsive to changesasdistinguished held energized by a holding circuit which is 35 from actual values,-it preferably comprises aconindependent of the main control switch. This 'trol element, such as a switch or a plurality of holding circuit is controlled by a switch responswitches, that isassociated witha device responsive to predetermined changes in some other 40 sive to actual values through the medium of the condition or force, or td-the effectiveness of the well known non-positive transmission means'or condition or force changing device being con- 40 slip-frictional, connection. trolled. After thelpredete'rmined change occurs, A further object of the invention is the-prothe relay is maintained energized by the main vision of a new method for controlling the'value controlling switch it it still be in closed positl n. of a condition or force which method includes Furthermore, the main controlling switch is inthe steps of placing a condition or force changing capable of initially 'energizing the relay unless 45 device into operation when a first condition or there has been a predetermined change in the -force reaches a given value, then maintaining other condition or force, or lathe-effectiveness operation of said condition or force changing of the condition -or iorce changing device. In deviceindependently of said first condition or this manner, everytime the' relay is energized, it

force until there is' a predetermined change in a will be held energized forat least a short period. 50 second condition or force or in the eifectiveness It is to be particularly noted, that this holding oi the condition or force changing device, and circuit'for the relay is not based upon absolute thereafter controlling the condition or force time, butisbased upon some condition or force 5 changing device in accordance with the value of having a relation to thecontrol system as a 5 said first condition or force. whole.

A further object of the invention therefore is the provision of asimple electrical control system which eliminates relay chatter by providing a temporary holding circuit which is controlled by some means having a definite relationship to the control System as a whole, as distinguished from a straight timed temporary holding circuit.

Further objects of the invention .will be found in the detailed description, the drawings and the claims.

For a more complete understanding of the invention, reference may be had to'the following description and the accompanying drawings 11- lustrative of one embodiment of the present invention and, in which:

Fig. 1 is a diagrammatic showing of a system constructed in accordance with the present invention,

Fig. 2 is a front view of one of the control devices used in the system of Fig. 1, and Fig. 3 is a sectional view taken about line 3-3 of". Fig. 2.

Referring first to Fig. 1 of the drawings, a condition or force changing device is herein shown as comprising a boiler II) which is provided with the usual stack pipe II. The boiler I0 is shown'as being fired by a coal stoker I2 of any well known construction which is operated by an on the electric stoker motor l3 in the usual manner.

The boiler Ill operates to supply a heating medium to a radiator I 4, located in the space to be heated, by means of a supply pipe l5. The fluid medium after passing through the radiator l4 returns to the boiler I 8 bymeans of a return pipe l6. It will be understood that this showing of the boiler l8 and radiator I4 is merely exemplary of one type of condition or force changing device or temperature changing means and that others could be substituted therefor without departing from the spirit of this invention. It will be further understood that this heating system should be supplied with the usual fixtures, such as traps, etc., as is wellknown in the art.

The stoker motor I3 is primarily controlled by a condition or force responsive device, indicatedgenerally at H, herein shown in the form of a thermostatic switch that preferably responds to the temperature of the space being heated. The stoker motor I3 is additionally controlled by a control device, generally indicated at l8, which responds to changes in another condition or force or responds to changes in .the effectiveness of the boiler i0, and is herein shown as comprising a slip friction switching mechanism responsive to changes in the temperature of the gases passing through the stack pipe II.

Turning now to Figs. 2 and 3, the slip friction switching mechanism, generally indicated at l8, comprises a casing 28 of substantially square configuration. To the rear wall of casing 20 is secured a cylindrical mounting member 2|, there being a washer or spacer 22 interposed between the cylindrical mounting member 2| and the rear wall of the casing 28. The cylindrical mounting memberdl may be secured to the rear wall of casing 20 in any suitable manner such as by peening over a reduced portion which extends through the casing 20 as indicated at 23. The outer end of mounting member 2| is provided with a reduced portion 24 over which is placed a tubular member 25, the tubular member 25 being secured to the mounting member M by any suitable means such-as by brazing. The tubular member 25 has a portion of its surface stamped inwardly to provide a pair of flanges 28 and 21.

. casing 20.

ing within casing 28, extends through mounting member 2| and is provided with a reduced portion 29 which extends through flange 26 and terminates between flanges 26 and 21. A metallic block 30 is suitablysecured to the end of reduced portion 29. ically coiled element 3| is secured to tubular member 25 by means of a screw 32, whereas its other end is secured to metallic block 30 by means of a screw 33. Excessive axial movement @f torsion rod 28 towards the left (as viewed in Fig. 3) is prevented by engagement of block 30 with the flange 26 while excessive axial movement in the other direction is prevented by a cotter pin 34 which extends through torsion rod 28 at a. point just within the casing 20. Preferably, a washer 35 is placed between cotter pin 34 and the inside surface of the back wall of Just within the casing 28 a stop member 36 is secured to torsion rod 28 by means of a set screw 31. The torsion'rod 28 further carries a switch A torsion rod 28, having one of its ends terminat- One end of a bimetallic helduced terminal portion 44 of torsion rod 28.

The friction washer 42 is received by a cup .45. The switch actuating arm 40 is resiliently clamped between the friction washers 4| 'and 42 by a coiled compression spring 46 which is held by a pair of spring retainers" and 48, one of which abuts the cup and the other of which abuts the stop member 36. It -will therefore be's'een that the switch actuating arm 40 is frictionally connected to-the torsion rod 28 whereby it may normally move in conformity with the torsion rod 28 but further movement of torsion rod 28 is allowed when switch actuating arm 40 reaches the limit of its motion in either direction.

In the lower portion of casing 20, a bracket 50 is secured by means of screws 5|. This bracket 50 supports a pair of adjustable stop screws 52 and 53 which respectively cooperate. with stop members 54 and 55 that are formed by bending over portions of the switch actuating arm 48. By

adjusting these stop screws 52 and 53, the switch actuating arm 40 can be limited to varied ranges of movement. The switch actuating arm 40 is further provided with a bent over portion 56 to which is secured three switch arms 51, 58 and 59. Itwill be noted that the switch arms 51, 58 and 59 are provided with suitable backing members 60, 5| and 62. The arrangement is such, as indicated in the drawings, that these various switch arms and backing members are electrically insulated one from the other. The switch arm 5! cooperates with a contact screw 63, the switch arm 58 cooperates with a contact screw 64, and the switch arm 59 cooperates with a contact screw 65. The contact screws 63, 64 and 65 are all supported by brackets 50 and are insulated therefrom in any suitable manner. The arrangement is such that switch arms 51 and 58 engage their contact screws 63 and 64 upon movement of the subjected to the temperature of the gases passing The parts are shown through the stack pipe ll.

. and 81.

in Fig. 2 in the position they assume aiter there has been a predetermined drop in stack temperature. Upon an increase in stack temperature, switch arm 51 is first .moved from engagement 5 with its contact screw 63 by its backing member 58. The switch arm 59 then engages its contact screw 65, and thereafter switch arm 58 is disengaged from its contact screw 54 by its backing member 6|. Upon continued rise in stack tem- 10 perature, the stop member 55 engages stop screw 53 whereby further movement of switch actuating arm 4|] is prevented but further movement of torsion rod 28 is allowed by reason of the slip friction connection heretofore described. Switch arm 59 will flex away from its backing member 82 to permit this additional movement of switch actuating arm 48. I

Upon decrease in stack temperature, stop member 55 will leave stop screw 53 and as the stack temperature continues to fall, the switch arm 58 will engage its contact screw 54 after which it will be flexed slightlyso that it moves awayirom its backing member 51a small amount. During this time, the backing member 82 has been moving towards switch arm 59 and upon continued stack temperature fall, the backing member 82 will move switch arm 59 from engagement with contact screw 65, Upon continued temperature fall, contact arm 51 will flex away from its backing member 88. It will be noted that the provision of backing members 58, 5| and 52, while allowing flexing of switch arms 51, 58 and 59 upon engagement with their respective contact screws 63, 54 and 65, provide for movingthese switch arms 51,

58- and 59 from engagement with the respective contacts in a definite order determined by the adjustment of contact screws 53, 84 and 55. Upon slight further stack temperature fall, the stop member 54 engages stop screw 52 whereupon '4 further rotation of switch operating arm'48 is prevented but the heretofore described slip con-, nection allows continued rotation p f torsion rod 28. Returning now to Fig. 1 of the drawings, the 45 room thermostat 11 comprises a bimetallic element 10 having one 0! its ends secured, and its other end carrying a contact blade 1|. Contact blade 1| is adapted,to engage a stationary or manually adjustable contact 12 when the temper- 5 ature to which bimetallic element 19 responds falls to some predetermined value.

The room thermostat l1 and the switching mechanisml8 control the stoker motor 13 through a relay, generally indicated at 18. The 55 relay 18 comprises an electromagnetic relay coil 14 which, upon energization, attracts an armature 15 and moves switch arms 18 and 11 into engagement with cooperating contacts 18 and 19. High voltage power is supplied by line wires 89 Low voltage power is supplied by a stepdown transformer 82 which is provided with a low voltage secondary 88 and a high voltage primary 84 tliat is connected to the line wires 80 and 81. v The remaining circuit connections will be described under the heading Operation.

Operation 94 to. the other line wire screw 65. The stack temperature will continue to fall but the parts of the switching mechanism l8 will stay'in the positions shown. After a time, since the stoker is not operating, the room or space temperature will fall so as to bring contact 5 blade 1| into engagement with contact 12. When this happens, relay coil 14 is energized by the following circuit: secondary 88 of'transformer 82, wire 85, wire 85, bimetallic element 10, contact blade 1|, contact 12, wire 81, switch arm 51, con- 10 tact screw 63, wire 89, wire9ll, relay coil 14 and wire 9| to the other side of secondary 83. Switch arms-18 and 11 are therefore moved into engagement with their respective contacts 18 and 19." Engagement of switch arm 11 with contact 19 15 establishes an energizing circuit for stoker motor i3 as follows: line wire 8|, wire 92, contact 19, switch/arm 11, wire 99, stoker motor i3 and wire 88. Engagement of switch arm 15 with contact 18 establishes a hold- 20 ing circuit for relay coil 14 which is independent of contact blade '11 and contact 12 of the room thermostat 11. This holding circuit is as follows: secondary 88, wire 85, wire 98. contact screw 64, switch arm 58, wire 91, wire 98, contact 25 18, switch arm 15, wire 99, relay coil 14 and wire .holding circuit therefor was established which Y is independent of contact blade 1i and contact 12. Therefore, it the contact blade 1i vibrates upon contact 12, the relay coil 14 will not be rapidly and intermittently energized and deener-' 35 gized. In other words, the well known difficulty of relay chattering which isever present in systems employing a single circuit sensitive switching mechanism has been eliminated by the provision of a holding circuit which is independent 40 of the sensitive switching mechanism.

The stack temperature will rise relatively rapidly as a result of operation of the stoker, and first operates to move switch arm 51 from engagement with contact screw 53. This interrupts the initial energizing circuit for relay coil 14 but the relay coil 14 is maintained energized by the above described holding circuit. Upon further rise in stack temperaturefthe switch arm 59 is brought into engagement with cantact screw 55. This completes a maintaining circuit for relay coil 14 which is as follows: secondary 83, wire 85, wire 85, bimetallic element 10, contact blade 1i, contact 12, wire 81 switch arm 59, contact screw 65, wire 99, wire' 98, contact 18, switch arm 16, wire 98, relay coil 14 and wire 91 to the other side of secondary 83. This maintaining circuit however 58 from engagement with contact screw 84 whereupon the holding circuit is interrupted. When this occurs, the control of the relay coil '14 is returned to the room thermostat.

Now if the room thermostat should break the maintaining circuit by moving contact blade 1| from engagement with contact 12, the relay coil 14 will be deenergized and even though contact blade 1| inm'lediately-reengages contact 12, the relay coil cannot again be energized until such time as the stack temperature has dropped suf- 7 flciently to first. move switch arm 58 into engagement with contact screw 64 then move switch arm 59 from engagement with contact screw and finally move switch arm 51 into engagement with contact screw 53. In this manner, it will 7 be seen that all possibility of relay chattering is obviated. Engagement of switch arm 58 with contact screw 54 prior to engagement of switch arm 51 with contact 63 is important since it conditions the holding circuit for completion prior to the time that it is possible to establish the initial energizing circuit. Likewise, engagement of switch arm 59 with contact screw 65 prior to disengagement of switch arm 58 from contact screw 64 upon stack temperature rise is important since this conditions the maintaining circuit for energization prior to the time that the holding circuit is interrupted and insures that the relay coil 14 will be returned to the control of the room thermostat immediately upon interruption of the holding circuit.

The provision of the temporary holding circuit forthe relay coil to eliminate relay chatter by means having a definite relation to the control system as a whole as distinguished from a purely time controlled holding circuit is one of the important features of the invention.

While a specific embodiment of the invention has been herein described, it will be clear that many changes in the details of the apparatus and system can be made without departing from the spirit of the invention and I therefore intend to be limited only by the scope of the appended claims. a

I claim:

1. In combination, a condition changing device, means for controlling the same, a main condition responsive element, a secondary condition responsive element responsive to predetermined changes in the value, irrespective of the actual value, of another condition which is produced directly by said condition changing device, connections between said elements and said condition changing device controlling means for placing the latter into operation by the conjoint action of said elements when the condition to which said main condition responsive element reaches a predetermined value and upon a predetermined change in the value, irrespective of the actual value, of. said other condition in one direction, connections between said secondary element and condition changing device controlling means for maintaining operation of the latter independently of the main condition responsive element until said other condition changes a predetermined amount in the other direction-,irrespective of the actual value of the condition, as a result of operation of said condition changing device controlling ,means, and other connections between said elemerits for thereafter returning the control of said condition changing device controlling means to, said main condition responsive element. I

2. In combination, a condition changing device, electromagnetic means for controlling the operation thereof, a holding switch moved to closed position upon energization of said electromagnetic means, a main controlling switch, switching means responsive to a condition directly produced by said, condition changing device, an energizing circuit for said electromagnetic means controlled by said main controlling switch and switching means, a holding circuit for said electromagnetic means independent of said main controlling switch controlled by said holding switch and switching means, and a maintaining circuit for said electromagnetic'means controlled by said main controlling switch and holding switch. r

3. In combination, a condition changing device,

75 electromagnetic means in control thereof, a holding switch moved to closed position upon ener- .gization of said electromagnetic means, a main controlling switch, first, second and third condition responsive switches, means responsive to a condition directly produced by said condition changing device in control of said switches for closing said third switch prior to opening said second switch upon change in the value of said condition in one direction and for closing said I first switch only after said second switch closes and said third switch opens upon change in the value of said condition in the opposite direction, an initial energizing circuit for said electromagnetic means controlled by said main controlling switch and first switch in series, a holding circuit for said electromagnetic means independent of said main controlling switch including said holding switch and second switch in series, and a maintaining circuit for said electromagnetic means including said main controlling switch, holding-switch and third switch in series.

4. In combination, a condition changing device, electromagnetic means in control thereof, a holding switch moved to closed position upon energization of said electromagnetic means, a main controlling switch, first, second and third condition responsive 'tches, means responsive to a condition directly roduced by said condition changing device in control of said switches for opening said first switch and then sequentially closing said third switch and opening said second switch upon change in the value of said condition in one direction and for closing said first switch only after said second switch closes and said ,third switch opens upon change in the value of said condition in the opposite direction, an initial energizing circuit for said electromagnetic means controlled by said main controlling switch and first switch in series, a holding circuit for said controlling switch, first, second and third condition responsive switches, means responsive to a condition directly produced by said temperature changing device in control of said switches for closing said third switch prior to opening said second switch upon change in the value of said condition in one direction and for closing said first switch only after said second switch closes and said third switch opens upon change in the value of said condition in the opposite direction, an initial energizing circuit for said electromagnetic means controlled by said main controlling switch and first switch in series, a holding circuit for said electromagnetic means independent of said main controlling switch including said holding switch andsecond switch in series, and a maintaining circuit for said electromagnetic means including said main controlling switch, holding switch and third switch in series.

6. In combination, a heater, electromagnetic means in control thereof, a holding switch moved to closed position upon energization of said electromagnetic means, a temperature responsive main controlling switch, first, second and third condition responsive switches, means responsive to a condition directly produced by said heater in control of said switches for closing'said third change in the value of said condition in one direction and for closing said first switch only Y after said second switchcloses and said third switch opens upon change in the value of said condition in the opposite direction, an initial energizing circuit for said electromagnetic means controlled by said main controlling switch and first switch in series, a holding circuit for said electromagnetic means independent of said main controlling switch including said holding switch and second switch-in series, and a maintaining circuit for said electromagnetic means including said main controlling switch, holding switch and third switch in series.

7. In combination, a heater, electromagnetic means for placing said heater in operation while energized, first, second and third switches, an element responsive to a heater condition for closing said third switch prior to opening said second switch upon an increase in said heater condition and for closing said first switch only after closure of said second switch and after opening of said third switch upon a decrease in said heater condition, a holding switch moved to closed position and held therein upon continued energization of said electromagnetic means, a space temperature responsive main switch, an initial energizing circuit for said electromagnetic means controlled by said main switch and said first switch, a holding circuit for said electromagnetic means controlled 'by said holding switch and second switch, and a maintaining circuit for said electromagnetic means controlled by said main switch, holding switch and third switch in series.

8. In combination, a heater, electromagnetic means for placing said heater in operation while energized, first, second and third switches, a thermostatic element responsive to a temperature' condition directly produced by said heater for closing said third switch before opening said second switch upon-an increase in said temperature condition and for closing said first switch 0 after closure of said second switch and after opening of said third switch upon a decrease in said temperature condition, a holding switch moved to closed position and held therein upon continued energization of said electromagnetic means, a space temperature main controlling switch, an initial energizing circuit for said electromagnetic means controlled by said main controlling switch and said first switch, a holding circuit for said electromagnetic means controlled by said holding switch and second switch, and a maintaining circuit 'for said electromagnetic means controlled by said main controlling switch, holding switch and third switch in series.

WILLIAM M. SCHWEICKART. 

